Bottom Line:
We found that stearic acid potentiated LDH-a-dependent production of lactate, which further stabilized HIF1α protein and increased VEGF and proinflammatory cytokine expression in primary mouse chondrocytes.Treatment with LDH-a and HIF1α inhibitors notably attenuated stearic acid-or high fat diet-stimulated proinflammatory cytokine production in vitro and in vivo.In conclusion, saturated free fatty acid induced proinflammatory cytokine production partly through activation of a novel lactate-HIF1α pathway in chondrocytes.

ABSTRACTThe biomechanics stress and chronic inflammation in obesity are causally linked to osteoarthritis. However, the metabolic factors mediating obesity-related osteoarthritis are still obscure. Here we scanned and identified at least two elevated metabolites (stearic acid and lactate) from the plasma of diet-induced obese mice. We found that stearic acid potentiated LDH-a-dependent production of lactate, which further stabilized HIF1α protein and increased VEGF and proinflammatory cytokine expression in primary mouse chondrocytes. Treatment with LDH-a and HIF1α inhibitors notably attenuated stearic acid-or high fat diet-stimulated proinflammatory cytokine production in vitro and in vivo. Furthermore, positive correlation of plasma lactate, cartilage HIF1α and cytokine levels with the body mass index was observed in subjects with osteoarthritis. In conclusion, saturated free fatty acid induced proinflammatory cytokine production partly through activation of a novel lactate-HIF1α pathway in chondrocytes. Our findings hold promise of developing novel clinical strategies for the management of obesity-related diseases such as osteoarthritis.

Mentions:
To explore whether the serum-derived factors are contributors of the chondrocyte inflammation, we collected the serum from the mice with a normal diet (ND) or HFD for 8 weeks. The full serum was then separated into a protein fraction (>3 KD) and a metabolite fraction (<3 KD) to treat the primary chondrocytes from the ND-feeding mice. Comparing to the full serum, protein fraction and metabolite fraction from the ND group, the ones from HFD group notably stimulated mRNA expression of IL-6 (Fig. 2a), TNF-α (Fig. 2b) and IL-1β (Fig. 2c). Unexpectedly, the mRNA expression of VEGF was induced by the HFD group-derived full serum and metabolite fraction but not by the protein fraction (Fig. 2d). While it has been proven that proinflammatory cytokines (TNF-α, IL-1β, etc) are present at high levels in the protein fraction of serum from the HFD-feeding mice56, the proinflammatory molecules in the metabolite fraction of the serum are still not well-known. We performed metabonomics analysis of the metabolite fraction with GC-TOF-MS (see Supplementary Table S1), and verified that at least two elevated metabolic molecules, stearic acid (a kind of saturated FFAs) and lactate in obesity, were functional stimulators of proinflammatory cytokine and VEGF production in primary chondrocytes (Fig. 2e~l). However, the molecular mechanism linking stearic acid and lactate to the cytokine production in chondrocytes will be further explored.

Mentions:
To explore whether the serum-derived factors are contributors of the chondrocyte inflammation, we collected the serum from the mice with a normal diet (ND) or HFD for 8 weeks. The full serum was then separated into a protein fraction (>3 KD) and a metabolite fraction (<3 KD) to treat the primary chondrocytes from the ND-feeding mice. Comparing to the full serum, protein fraction and metabolite fraction from the ND group, the ones from HFD group notably stimulated mRNA expression of IL-6 (Fig. 2a), TNF-α (Fig. 2b) and IL-1β (Fig. 2c). Unexpectedly, the mRNA expression of VEGF was induced by the HFD group-derived full serum and metabolite fraction but not by the protein fraction (Fig. 2d). While it has been proven that proinflammatory cytokines (TNF-α, IL-1β, etc) are present at high levels in the protein fraction of serum from the HFD-feeding mice56, the proinflammatory molecules in the metabolite fraction of the serum are still not well-known. We performed metabonomics analysis of the metabolite fraction with GC-TOF-MS (see Supplementary Table S1), and verified that at least two elevated metabolic molecules, stearic acid (a kind of saturated FFAs) and lactate in obesity, were functional stimulators of proinflammatory cytokine and VEGF production in primary chondrocytes (Fig. 2e~l). However, the molecular mechanism linking stearic acid and lactate to the cytokine production in chondrocytes will be further explored.

Bottom Line:
We found that stearic acid potentiated LDH-a-dependent production of lactate, which further stabilized HIF1α protein and increased VEGF and proinflammatory cytokine expression in primary mouse chondrocytes.Treatment with LDH-a and HIF1α inhibitors notably attenuated stearic acid-or high fat diet-stimulated proinflammatory cytokine production in vitro and in vivo.In conclusion, saturated free fatty acid induced proinflammatory cytokine production partly through activation of a novel lactate-HIF1α pathway in chondrocytes.

ABSTRACTThe biomechanics stress and chronic inflammation in obesity are causally linked to osteoarthritis. However, the metabolic factors mediating obesity-related osteoarthritis are still obscure. Here we scanned and identified at least two elevated metabolites (stearic acid and lactate) from the plasma of diet-induced obese mice. We found that stearic acid potentiated LDH-a-dependent production of lactate, which further stabilized HIF1α protein and increased VEGF and proinflammatory cytokine expression in primary mouse chondrocytes. Treatment with LDH-a and HIF1α inhibitors notably attenuated stearic acid-or high fat diet-stimulated proinflammatory cytokine production in vitro and in vivo. Furthermore, positive correlation of plasma lactate, cartilage HIF1α and cytokine levels with the body mass index was observed in subjects with osteoarthritis. In conclusion, saturated free fatty acid induced proinflammatory cytokine production partly through activation of a novel lactate-HIF1α pathway in chondrocytes. Our findings hold promise of developing novel clinical strategies for the management of obesity-related diseases such as osteoarthritis.